The present invention relates to a sample and hold circuit for storing an analogue voltage level. More specifically, the invention relates to a sample and hold circuit that can be integrated on a substrate.
Smith, U.S. Pat. No. 3,551,698, describes an analogue memory system that uses a capacitive element to store a signal in the form of electric charge, indicated by the voltage across the capacitive element. A follower circuit receives the voltage across the capacitor and feeds back its output to one side of the switch used to charge the capacitive element. This reduces leakage of the stored charge, so that the signal is stored for an extended time. As shown and described in relation to FIG. 1, Smith's follower circuit includes a high impedance coupling circuit, such as a MOSFET; a two-stage differential amplifier; a gain control circuit; and an output circuit. As shown and described in relation to FIG. 3, a tubular-type capacitor and a separate MOSFET are mounted on a board.
Viswanathan, U.S. Pat. No. 4,783,602, describes an integrated circuit that includes an operational transconductance amplifier (OTA) for use in sample and hold circuits, shown and described in relation to FIG. 1. When the OTA is used in a sample and hold circuit, as shown and described in relation to FIG. 2, it is on stand-by during the hold mode, and essentially no leakage current flows to or from the OTA, so that the output of the operational output amplifier does not change.